What's missing from the accounts is why he had those plates there in the first place.
Why was he placing plates streaked with staphylococcus near a window and then peering at them every few days?
Perhaps he was testing some other hypothesis that didn't turn out? The effect of sunlight on staphylococcal growth, maybe? Or perhaps the window is simply incidental?
He only noticed after he got back from vacation, or so the story goes. And it may not have been an open window, could have been a desk near the doorway.
